Imprints of primordial non-Gaussianity on the number counts of cosmic shear peaks

We studied the effect of primordial non-Gaussianity with varied bispectrum shapes on the number counts of signal-to-noise peaks in wide field cosmic shear maps. The two cosmological contributions to this particular weak lensing statistic, namely the chance projection of Large Scale Structure and the occurrence of real, cluster-sized dark matter halos, have been modeled semi-analytically, thus allowing to easily introduce the effect of non-Gaussian initial conditions. We performed a Fisher matrix analysis by taking into account the full covariance of the peak counts in order to forecast the joint constraints on the level of primordial non-Gaussianity and the amplitude of the matter power spectrum that are expected by future wide field imaging surveys. We find that positive-skewed non-Gaussianity increases the number counts of cosmic shear peaks, more so at high signal-to-noise values, where the signal is mostly dominated by massive clusters as expected. The increment is at the level of ~1 for f_NL=10 and ~10 for f_NL=100 for a local shape of the primordial bispectrum, while different bispectrum shapes give generically a smaller effect. For a future survey on the model of the proposed ESA space mission Euclid and by avoiding the strong assumption of being capable to distinguish the weak lensing signal of galaxy clusters from chance projection of Large Scale Structures we forecasted a 1-sigma error on the level of non-Gaussianity of ~30-40 for the local and equilateral models, and of ~100-200 for the less explored enfolded and orthogonal bispectrum shapes.Comment: 13 pages, 8 figures, 1 table. Submitted to MNRA

Strong lensing in the MareNostrum Universe II: scaling relations and optical depths

The strong lensing events that are observed in compact clusters of galaxies can, both statistically and individually, return important clues about the structural properties of the most massive structures in the Universe. Substantial work is ongoing in order to understand the degree of similarity between the lensing cluster population and the population of clusters as a whole, with members of the former being likely more massive, compact, and substructured than members of the latter. In this work we exploit synthetic clusters extracted from the {\sc MareNostrum Universe} cosmological simulation in order to estimate the correlation between the strong lensing efficiency and other bulk properties of lensing clusters, such as the virial mass and the bolometric X-ray luminosity. We found that a positive correlation exist between all these quantities, with the substantial scatter being smaller for the luminosity-cross section relation. We additionally used the relation between the lensing efficiency and the virial mass in order to construct a synthetic optical depth that agrees well with the true one, while being extremely faster to be evaluated. We finally estimated what fraction of the total giant arc abundance is recovered when galaxy clusters are selected according to their dynamical activity or their X-ray luminosity. Our results show that there is a high probability for high-redshift strong lensing clusters to be substantially far away from dynamical equilibrium, and that $30-40\%$ of the total amount of giant arcs are lost if looking only at very X-ray luminous objects.Comment: 15 pages, 10 figures. Accepted by A&

The effect of primordial non-Gaussianity on the skeleton of cosmic shear maps

(abridged) We explore the imprints of deviations from Gaussian primordial density fluctuations on the skeleton of the large-scale matter distribution as mapped through cosmological weak lensing. We computed the skeleton length of simulated effective convergence maps covering $\sim 35$ sq. deg each, extracted from a suite of cosmological $n-$body runs with different levels of local primordial non-Gaussianity. The latter is expected to alter the structure formation process with respect to the fiducial Gaussian scenario, and thus to leave a signature on the cosmic web. We found that alterations of the initial conditions consistently modify both the cumulative and the differential skeleton length, although the effect is generically smaller than the cosmic variance and depends on the smoothing of the map prior to the skeleton computation. Nevertheless, the qualitative shape of these deviations is rather similar to their primordial counterparts, implying that skeleton statistics retain good memory of the initial conditions. We performed a statistical analysis in order to find out at what Confidence Level primordial non-Gaussianity could be constrained by the skeleton test on cosmic shear maps of the size we adopted. At 68.3% Confidence Level we found an error on the measured level of primordial non-Gaussianity of $\Delta f_\mathrm{NL}\sim 300$, while at 90% Confidence Level it is of $\Delta f_\mathrm{NL}\sim 500$. While these values by themselves are not competitive with the current constraints, weak lensing maps larger than those used here would have a smaller field-to-field variance, and thus would likely lead to tighter constraints. A rough estimate indicates $\Delta f_\mathrm{NL} \sim$ a few tens at 68.3% Confidence Level for an all-sky weak lensing survey.Comment: 11 pages, 9 figures. Accepted for publication on MNRA

Particle acceleration and radiation friction effects in the filamentation instability of pair plasmas

The evolution of the filamentation instability produced by two counter-streaming pair plasmas is studied with particle-in-cell (PIC) simulations in both one (1D) and two (2D) spatial dimensions. Radiation friction effects on particles are taken into account. After an exponential growth of both the magnetic field and the current density, a nonlinear quasi-stationary phase sets up characterized by filaments of opposite currents. During the nonlinear stage, a strong broadening of the particle energy spectrum occurs accompanied by the formation of a peak at twice their initial energy. A simple theory of the peak formation is presented. The presence of radiative losses does not change the dynamics of the instability but affects the structure of the particle spectra.Comment: 8 pages, 8 figures, submitted to MNRA

Selection effects on X-ray and strong-lensing clusters in various cosmologies

Galaxy clusters are hotter and more X-ray luminous than in quiescence while they undergo major mergers, which also transiently increase their strong-lensing efficiency. We use semi-analytic models for both effects to study how cluster dynamics in different dark-energy models affects the X-ray selected cluster population and its strong-lensing optical depth. We find that mergers increase the number of observable X-ray clusters by factors of a few and considerably broaden their redshift distribution. Strong-lensing optical depths are increased by a very similar amount. Quite independent of cosmology, X-ray bright clusters above a flux limit of $10^{-13.5} \mathrm{erg s^{-1} cm^{-2}}$ produce $\sim60$ of the strong-lensing optical depth, and only $\sim1$ above a flux limit of $10^{-11.5} \mathrm{erg s^{-1} cm^{-2}}$ if mergers are taken into account.Comment: 11 pages, 9 figures. Version accepted by A&

The strongest gravitational lenses: I. The statistical impact of cluster mergers

For more than a decade now, it has been controversial whether or not the high rate of giant gravitational arcs and the largest observed Einstein radii are consistent with the standard cosmological model. Recent studies indicate that mergers provide an efficient mechanism to substantially increase the strong-lensing efficiency of individual clusters. Based on purely semi-analytic methods, we investigated the statistical impact of cluster mergers on the distribution of the largest Einstein radii and the optical depth for giant gravitational arcs of selected cluster samples. Analysing representative all-sky realizations of clusters at redshifts z < 1 and assuming a constant source redshift of z_s = 2.0, we find that mergers increase the number of Einstein radii above 10 arcsec (20 arcsec) by ~ 35 % (~ 55 %). Exploiting the tight correlation between Einstein radii and lensing cross sections, we infer that the optical depth for giant gravitational arcs with a length-to-width ratio > 7.5 of those clusters with Einstein radii above 10 arcsec (20 arcsec) increases by ~ 45 % (85 %). Our findings suggest that cluster mergers significantly influence in particular the statistical lensing properties of the strongest gravitational lenses. We conclude that semi-analytic studies must inevitably take these events into account before questioning the standard cosmological model on the basis of the largest observed Einstein radii and the statistics of giant gravitational arcs.Comment: 23 pages, 18 figures; accepted for publication in Astronomy and Astrophysics; v2: minor corrections (added clarifying comments; added Fig. 19) to match the accepted versio

A hybrid asymptotic-FVTD method for the estimation of the radar cross section of 3D structures

The Finite Volume Time-Domain (FVTD) method is an effective full-wave technique which allows an accurate computation of the electromagnetic field. In order to analyze the scattering effects due to electrically large structures, it can be combined with methods based on high-frequency approximations. This paper proposes a hybrid technique, which combines the FVTD method with an asymptotic solver based on the physical optics (PO) and the equivalent current method (ECM), allowing the solution of electromagnetic problems in the presence of electrically large structures with small details. Preliminary numerical simulations, aimed at computing the radar cross section of perfect electric conducting (PEC) composite objects, are reported in order to evaluate the effectiveness of the proposed method

Electron heating in subpicosecond laser interaction with overdense and near-critical plasmas

n this work we investigate electron heating induced by intense laser interaction with micrometric flat solid foils in the context of laser-driven ion acceleration. We propose a simple law to predict the electron temperature in a wider range of laser parameters with respect to commonly used existing models. An extensive two-dimensional (2D) and 3D numerical campaign shows that electron heating is due to the combined actions of j×B and Brunel effect. Electron temperature can be well described with a simple function of pulse intensity and angle of incidence, with parameters dependent on pulse polarization. We then combine our model for the electron temperature with an existing model for laser-ion acceleration, using recent experimental results as a benchmark. We also discuss an exploratory attempt to model electron temperature for multilayered foam-attached targets, which have been proven recently to be an attractive target concept for laser-driven ion acceleration